Method and arrangement for quenching a braking thyratron for motors

ABSTRACT

A supply and control circuit for a DC motor having a separately excited field coil and armature, and a method of operating such circuit. The field coil and armature are supplied with current interrupters. Connected in parallel with the separately excited field coil of the motor there is a first thyristor which plays a &#39;&#39;&#39;&#39;free wheeling&#39;&#39;&#39;&#39; role. A second circuit connected in parallel with the field coil includes an inductance, a second thyristor, and a zener diode connected in series. A condenser is connected in parallel with the zener diode. A diode is connected in parallel with the inductance and first thyristor. The parts are so arranged that the firing of the principal thyristor of the current interrupter for the field coil of the motor, after the operation of braking the motor, produces the extinction of the second thyristor, thereby bringing the current flow in the field coil to zero. When the current flow has been restored to its positive value and attains a predetermined potential, the principal thyristor in the interrupter which supplies the armature of the motor with current may be fired to restore the functioning of the motor as a driving motor.

United States Patent Mar. 21, 1972 Vidal et a1.

[54] METHOD AND ARRANGEMENT FOR QUENCHING A BRAKINGTHYRATRON FOR MOTORS[72] Inventors: Gilbert Vidal, Draveil; Bernard Peron, Villetaneusc,both of France [73] Assignee: Societe Generale de ConstructionsElectriques et Mechaniques (Alsthom), Paris, France [22] Filed: Apr. 14,1970 21 Appl. No.: 28,319

301 Foreign Application Priority Data Apr. 14, 1970 France ..69l1898[52] US. Cl .318/269, 318/379 [51] Int. Cl. ..H02p 3/12 [58] Field ofSearch ..318/2 58, 269, 379, 380;

[56] References Cited UNITED STATES PATENTS 3,222,587 12/1965 Lichowsky..318/38O 3,325,714 6/1967 Torii ..318/269 3,344,324 9/1967 Morris..3l8/258 3,447,054 5/1969 Hansen et a1. ..318/269 PrimaryExaminer-Bernard A. Gilheany Assistant Examiner-W. E. Duncanson, Jr.

AtrorneyArthur O. Klein [5 7] ABSTRACT A supply and control circuit fora DC motor having a separately excited field coil and armature, and amethod of operating such circuitLThe field coil and armature aresupplied with current interrupters. Connected in parallel with theseparately excited field coil of the motor there is a first thyristorwhich plays a free wheeling" role. A second circuit connected inparallel with the field coil includes an inductance, a second thyristor,and a zener diode connected in series. A condenser is connected inparallel with the zenerdiode. A diode is connected in parallel with theinductance and first thyristor, The parts are so arranged that thefiring of the principal thyristor of the current interrupter for thefield coil of the motor, after the operation of braking the motor,produces the extinction of the second thyristor, thereby bringing thecurrent flow in the field coil to zero. When the current flow has beenrestored to its positive value and attains a predetermined potential,the principal thyristor in the interrupter which supplies the armatureof the motor with current may be fired to restore the functioning of themotor as a driving motor.

5 Claims, 2 Drawing Figures PATENTEDMAR'ZI m2 3.651.390

INVENTO R5 G4 beam" VI DAL BeaNRKO PERON wma/@* ATTo an av METHOD ANDARRANGEMENT FOR QUENCHING A BRAKING THYRATRON FOR MOTORS This inventionrelates to a variable braking system for a DC driving motor having aseparate source of excitation. More precisely, the motor with whichtheinvention is concerned is fed by the intermediary of currentinterrupters in both the circuits which supply the armature and thefield winding, respectively. During braking, the motor functions as agenerator of a reverse potential, designated the braking potential,through the intermediary of a thyristor, designated a braking thyristor.

Each of the current interrupters comprises a principal thyristor, athyristor for quenching the principal thyristor, an inductance and aswitching condenser, and a thyristor or rectifier for charging suchcondenser.

The invention is particularly adapted for application to road vehicleshaving electrical motors separately excited and fed by storage batteriesor consumable batteries, and railroad vehicles driven by electric motorshaving separate excitation.

The braking thyristor, which is connected in series with the brakingpotential, must be able to be extinguished at least at the end of thebraking period; thishas required, in previously known systems, the useof an extinction thyristor, a switching inductance and a switchingcondenser, and athyristor for recharging the switching condenser, aswell as a choke coil and a decoupling condenser. This has rendered thesystem quite bulky and costly.

The present invention makes it possible to eliminate the circuitelements previously connected to the braking thyristor; to

accomplish such result, at the end of the braking period there is abrief reversal of the direction of the current for exciting the drivingmotor; this causes an inversion in the polarity of the current appliedto the terminals of the motor, and as a result, produces extinction ofthe braking thyristor.

Such momentary inversion of the exciting current for the motor can beproduced in a known circuit, for example, wherein the field coil of themotor is fed through the intermediary of a thyristor bridge.

The system according to the invention provides a particularly simplearrangement for effecting such inversion of the current which feeds thefield of the motor. In accordance with the invention, there is connectedin parallel with the field of the motor a first thyristor whichis ableto play a free wheeling" role, and on the other hand, there is employeda condenser which is mounted in parallel with a voltage limiter such asa zener diode. Connected between the current interrupter which feeds thefield of the motor and the parallel connected voltage limiter andcondenser are two branch lines, the first of which includes a secondthyristor connected in series with an inductance, and the second ofwhich includes a diode, the direction of connection of the secondthyristor being such that it is connected by its anode and its cathodeto the cathode and the anode, respectively, of the first thyristor. Theinductance in series with the second thyristor is strongly coupled withthe switching inductance of the current interrupter for supplying thefield of the motor; the parts are so connected that when the principalthyristor of such current interrupter fires, the second thyristor isextinguished.

With the aid of the accompanying drawings, there is described apreferred embodiment of the system of the present invention.

In such drawings:

FIG. 1 is a circuit diagram of a prior art system for braking aseparately excited direct current motor; and

FIG. 2 shows a circuit diagram of'a system in accordance with thepresent invention.

In the prior art system shown in FIG. 1, the DC motor 1 has its armature2 fed by a source of direct current (not shown) which is connected toplus and minus terminals 3 and 4 of main wires A and B, respectively,through the intermediary of a current interrupter 5. The field coil 6 ofthe motor 1 is fed through the intermediary of a current interrupter 7.Connected across the terminals of the armature 2 is a free wheeling"diode 8, and connected across the terminals of the field coil 6 of themotor is a free wheeling diode 9.

The current interrupter consists of a principal thyristor l0, aswitching inductance 11, a switching condenser 12, a

thyristor 13 for extinguishing the principal thyristor l0, andathyristor 14 for recharging the condenser 12. Likewise, the currentinterrupter 7 consists of a principal thyristor 15, a switchinginductance 16, a switching condenser 17, a thyristor 18 forextinguishing the principal thyristor l5, and a rectifier 19 forcharging the condenser 17. The junction between inductance l6 and fieldcoil 6 is designated 34.

When the motor 1 is being braked, the motor functions as a generator ofa reverse braking potential, such oppositely directed potential beingimposed upon a resistor 20 by means of a braking thyristor 21. Thecircuit of the thyristor 21 includes a switching inductance 22, aswitching condenser 23, an extinguishing thyristor 24, and a thyristorfor charging the condenser 23, the thyristors 24 and 25 being reverselyconnected in parallel, as shown. It is also necessary to employ a chokecoil 26 and a condenser 27.

In the circuit of the invention shown in FIG. 2 the same elements arefound as those in FIG. 1 with the exception that there have been omittedfrom the circuit of the extinction thyristor 21 the following elements:the inductance 22, the condenser 23, thyristors 24 and 25, as well asthe choke coil 26 and the condenser 27. The following elements have beenadded to the circuit of FIG. 1: a thyristor 28 is connected betweenjunction 34 and wire B. A first line 35, extending from the junction 34to the wire B, has the following elements connected in series: aninductance 32, the anode of a thyristor 31, the cathode of such athyristor, the anode of a zener diode 30, and the cathode of such zenerdiode. A second line 36, which extends from line 35 in advance of thezener diode 30 to the wire B, has a condenser 29 interposed therein. Athird line 37 extends from junction 34 to the cathode of a diode 33, theanode of such diode being connected to the line 36 in advance of .thecondenser 29. As indicated by the curved arrow in FIG. 2, theinductances l6 and 32 are closely magnetically coupled to each other.

The illustrative circuit (FIG. 2) of the invention operates as follows:When the motor 1 is being driven, the current interrupters 5 and 7regulate the amount of current fed to the armature 2 and the field coil6, respectively, by firing or rendering conductive the thyristors l0 and15 for a predetermined time so as to feed the armature 2 and field 6from the current source 3, 4. When it is desired to brake the motor 1,the thyristor 10 is not refired, and the braking thyristor 21 is fired,the current interrupter 7 continuing to function. During the driving ofthe motor 1, and also during its functioning while being braked, thethyristor 28 is fired at the same time that the thyristor 15 isextinguished and the thyristor 18 is fired, so that the thyristor 28plays the role of a free wheeling diode. The thyristor 28 isextinguished when the thyristor 15 is refired.

At the end of the braking period, it is necessary, in accordance withthe invention, momentarily to reverse the direction of current passingthrough the field coil 6. To accomplish this, the thyristor 15 is notfired any longer, nor is the thyristor 28 fired. The current circulatingin the field coil 6 charges the condenser 29 through the diode 33 up tothe potential which is determined by the voltage limiting device, thatis, the zener diode 30. The thyristor 31 is then fired; this permits thecondenser 29 to discharge by passing through field coil 6 a current inthe opposite direction fromthat, which we shall call positive, whichpasses through it during both its being driven and being braked. Therethus results an inversion of the polarity of the voltage generated bythe motor 1 and thus an inversion of the polarity at the terminals ofthe thyristor 21, thereby producing an extinction of such thyristor.

When motor 1 is again to be driven, the thyristor 15 is fired; this, bythe coupling effect between the coils l6 and 32 causes extinction of thethyristor 31. The current in the field coil 6 is thereby annulled. Whenthe current in the field coil 6 regains its positive value and attains apredetermined potential, the thyristor 10 may be fired in order torestore the functioning of the motor 1 as a driving motor by supplyingcurrent to armature 2 through interrupter 5.

Although the invention is illustrated and described with reference toone preferred embodiment thereof, it is to be understood that it is inno way limited to the disclosure of such a preferred embodiment, but iscapable of numerous modifications within the scope of the appendedclaims.

What is claimed is:

1. In a method of operating a DC motor wherein the motor is driven byseparately exciting its field coil and armature with a first polarityvia intermittent pulses and wherein the motor is dynamically braked byterminating the armature excitation and simultaneously coupling a loadacross the armature terminals by operating a suitably disposed thyristorgate forwardbiased when the armature voltage has the first polarity, animproved technique for terminating such dynamic braking, whichcomprises:

reversing the polarity of excitation of the field coil to reverse thearmature voltage polarity, thereby removing the forward bias on thethyristor gate to decouple the load from the armature. 2. A method asdefined in claim 1, in which the reversal of polarity is accomplishedby:

terminating the excitation of the field coil while the armature iscoupled to the load; I

externally storing the energy represented by the current flowing throughthe field coil when its excitation is terminated; and

passing a current derived from such stored energy through the field coilin a direction opposite to the direction of current therethrough whenits excitation is terminated.

3. A method as defined in claim 2, further comprising the simultaneoussteps of terminating the derived current and reexciting the field coilwith the first polarity.

4. In combination with a DC motor having a field coil and an armature:

first normally unoperated, unidirectional switching means operable toexcite the field coil with a first polarity;

second normally unoperated, unidirectional switching means operable toexcite the armature with the first polarity;

a nonnally unoperated thyristor gate having a transconductive pathinterconnecting the armature with a load, the thyristor gate being poledto pass current from the armature to the load when the annature isexcited with the first polarity;

a capacitor; 1

a charging path including a diode serially interconnecting the fieldcoil and the capacitor, the diode being poled to be forward-biased whenthe field coil is excited with the first polarity; and

a discharge path including third nonnally unoperated, unidirectionalswitching means serially interconnecting the field coil and thecapacitor, the third switching means being poled to pass current throughthe field coil in a direction opposite to that passed when the fieldcoil is excited with the first polarity.

5. The combination as defined in claim 4, further comprising means fordisabling the third switching means upon operation of the firstswitching means.

1. In a method of operating a DC motor wherein the motor is driven byseparately exciting its field coil and armature with a first polarityvia intermittent pulses and wherein the motor is dynamically braked byterminating the armature excitation and simultaneously coupling a loadacross the armature terminals by operating a suitably disposed thyristorgate forward-biased when the armature voltage has the first polarity, animproved technique for terminating such dynamic braking, whichcomprises: reversing the polarity of excitation of the field coil toreverse the armature voltage polarity, thereby removing the forward biason the thyristor gate to decouple the load from the armature.
 2. Amethod as defined in claim 1, in which the reversal of polarity isaccomplished by: terminating the excitation of the field coil while thearmature is coupled to the load; externally storing the energyrepresented by the current flowing through the field coil when itsexcitation is terminated; and passing a current derived from such storedenergy through the field coil in a direction opposite to the directionof current therethrough when its excitation is terminated.
 3. A methodas defined in claim 2, further comprising the simultaneous steps ofterminating the derived current and re-exciting the field coil with thefirst polarity.
 4. In combination with a DC motor having a field coiland an armature: first normally unoperated, unidirectional switchingmeans operable to excite the field coil with a first polarity; secondnormally unoperated, unidirectional switching means operable to excitethe armature with the first polarity; a normally unoperated thyristorgate having a transconductive path interconnecting the armature with aload, the thyristor gate being poled to pass current from the armatureto the load when the armature is excited with the first polarity; acapacitor; a charging path including a diode serially interconnectingthe field coil and the capacitor, the diode being poled to beforward-biased when the field coil is excited with the first polarity;and a discharge path including third normally unoperated, unidirectionalswitching means serially interconnecting the field coil and thecapacitor, the third switching means being poled to pass current throughthe field coil in a direction opposite to that passed when the fieldcoil is excited with the first polarity.
 5. The combination as definedin claim 4, further comprising means for disabling the third switchingmeans upon operation of the first switching means.